A checklist is the only field that applies only to the item you’re working on, instead of the whole collection. To add a checklist, click the "+ Add" button at the bottom of any item then "Add Checklist".
To add items to a checklist, expand your item to the details view. Click "Add Item" at the bottom of your checklist.
To delete an item, hover over it and click on the "x" that appears at the end.
To change the order of the items on your checklist, just drag and drop them into the right positions. If you have multiple checklists on a single item, you can also drag checklist items between the checklists! Just make sure you drag the item over where it says "Add item". To check an item off once it's done, click the checkbox next to its name. The % ticker in the top right corner of the checklist will update to show how much progress has been made.
You can also see the % ticker on items in Kanban, list, mind map and calendar view.
To hide checked items, click on the checklist name and open the checklist options menu. Click the toggle next to "Hide checked items".